All existing instant messaging systems can transfer files. Thus, a user of an instant messaging system may send a file to a friend or receive a file from a friend, wherein a basic process is that:
(1) a sender sends a file transfer request to a receiver, then waits for a response of the receiver;
(2) after an instant messaging client of the receiver receives the file transfer request, the client prompts the receiver user on the screen to receive the file, and after the receiver user clicks on a receiving button to confirm to receive, the receiver sends the sender a response to agree to receive;
(3) after receiving the response to agree to receive, the sender starts to transmit the file to the receiver;
(4) during the file transfer, if a network connection is accidentally interrupted, then after detecting the transfer disconnection, the sender prompts the sender user to retransfer or to resumption of the transfer, and after the sender user clicks on a retransfer or resuming-transfer button, the sender sends the receiver a retransfer or resuming-transfer request;
(5) after the receiver detects the transfer disconnection, the receiver user is prompted of the transfer disconnection; after the receiver detects the retransfer or resuming-transfer request from the sender, the receiver user is prompted whether to agree to retransfer or to resumption of the transfer; after the receiver user confirms, a retransfer or resuming-transfer response is sent to the sender;
(6) when receiving a response from the sender to agree to retransfer or resumption of the transfer, the receiver retransfers the file, or resumes the transfer of the interrupted file to the sender.
On-line file transfer refers to file transfer through a network connection established directed between the sender and the receiver when both the sender and the receiver of the file are online. Off-line file transfer refers to that when the receiver of the file is offline, the file to be transferred is stored by a server, and is forwarded by the server to the receiver after the receiver goes online.
In such a way, file transfer between friends can be implemented. In a case of a poor network environment in which the transfer is susceptible to interruption, the existing instant messaging system requires manual confirmation from both the sender and the receiver to determine whether a retransfer or resumption of the transfer is needed. The retransfer refers to transferring the whole file once again, whereas the resumption of the transfer refers to resumption of the transfer at a point of interruption, namely, transfer of the remaining part that is not transferred is continued at a location of interruption based on the transferred part of the file.
However, when the transfer is interrupted frequently due to poor network environment, the file sender has to initiate a file sending operation frequently; meanwhile, the file receiver has to initiate a file receiving operation frequently, which is very inconvenient for users. Particularly, when a user at one party is not on scene, the file transfer is unable to be completed.
Therefore, in case of a poor network environment, too much manual intervention is required when file transfer by an existing instant messaging software encounters a network connection interruption, leading to a low transfer efficiency.